At present, various types of contents such as music, images, and documents are digitalized, and because of such digitalization, the content can be easily copied, and above all, it is a problem of illegal copy that causes a serious concern.
If an illegal copy equivalent to infringement of the copyright goes into circulation, not only the distributor and the copyright holder suffers from a loss, but also the consumer is unfavorably affected. For this reason, the content of higher value is required to be made use of under the system environment of the digital copyright management mounted with a copy right management function.
Usually, in the digital copyright management system, the content is encrypted, and the encrypted content and its encryption key are distributed to an access right owner who is given a permit to access the encrypted content. The access right owner stores the encrypted content and the encryption key into one device, and when accessing, performs the decryption of the encrypted content by using the encryption key, and then, accesses the content.
Further, when an access is desired to be made to the content by another device, it is necessary to transfer the encrypted content and the encryption key to another device. However, in order to prevent the content from being copied, a mechanism is adapted to control in such a manner that at least a pair of encryption key and encrypted content is not stored in a plurality of devices at the same time.    Patent Document 1: Japanese Patent Application Laid-Open No. 2000-134193    Patent Document 2: Japanese Patent Application Laid-Open No. 2000-285028
However, in such conventional digital copy right management system, when the access right owner tries to access the content acquired by a different device according to needs, it is necessary to transfer a pair of encryption key and encrypted content to the device in advance, and this hampers the usability of the user.
As a solution to cope with this problem, there is a method of using a server that performs key management, that is, a key management server. The access owner stores an encrypted content in a plurality of devices. At a point of time when the content is accessed, first, the owner accesses the key management server, and transfers the encryption key to the devices from the key management server or copies the encryption key with a time limit, and decodes the encrypted content by using this encryption key.
When the encryption key is transferred, the encryption key is returned to the key management server after the use is discontinued. When a copy is taken with a time limit, the encryption key becomes unusable after the set period of time elapses.
However, in the method of using the key management server, there is a problem that the key management server is absolutely necessary and that the communication with the key management server is absolutely necessary when the access is made to the content.
On the other hand, even in the field of Television Broadcasting, to prevent the problem of outflow into the internet of illegal copies readily made accompanied with the start of the digital broadcasting, the BS digital and terrestrial digital broadcasting programs in Japan have introduced the copy control signal CCI (Copy Control Information) to realize the [copy once] which permits video recording one time only from Apr. 1, 2004.
However, the content received and recorded in a hard disk drive and the like by HDTV (High Definition Television) resolution is put into a state of “copy once” by one time recording, and is applied with a copy protection. Consequently, when such content is once transferred to memory cards such as SD card by being transcoded into low resolution of QVGA (Quarter Video Graphic Array) of 320×240 pixels in order to watch by mobile terminal, the original HDTV content is eliminated when transferred. Hence, even when the QVGA content of the memory card is returned to the hard disk drive later, it cannot be restored to the original HDTV resolution, and the broadcast content of the HDTV resolution applied with protection of the copy once is lost, and cannot be reproduced again, thereby causing a problem.
An object of the present invention is to provide a content management program, method and device capable of taking a copy of one content and making it accessible for a plurality of devices, while maintaining constraint of a copy right use of copy once.